1. Field of the Invention
The present invention relates to an X-ray CT apparatus, and particularly to an X-ray CT apparatus configured to take an X-ray CT scan while rotating an annular rotor holding an X-ray tube and an X-ray detector.
2. Description of the Related Art
As described in JP-A No. 2002-172112 (KOKAI), for instance, there has been known an X-ray CT apparatus including an annular rotor which holds an X-ray tube and an X-ray detector, and which is rotatably supported by a stator with a bearing interposed therebetween. The diameter of the bearing rotatably supporting the rotor is set almost equal to the diameter of a diagnosis opening portion which is formed inside the rotor. This X-ray CT apparatus takes an X-ray CT scan of a subject by: positioning the subject inside the diagnosis opening portion; subsequently emitting X-rays onto the subject from the X-ray tube while rotating the rotor around the subject; and detecting the X-rays transmitted through the subject by the X-ray detector.
Furthermore, as described in JP-A No. Hei 02-200251 (KOKAI), there has been known an X-ray CT apparatus which includes a tilt mechanism configured to tilt its rotor at a desired tilt angle. The X-ray CT apparatus including the tilt mechanism is capable of taking X-ray CT scans of a subject at various angles by tilting the rotor at desired tilt angles by use of the tilt mechanism.
In the foregoing X-ray CT apparatuses, however, no considerations have been given to the following points.
In these years, a rotational speed of a rotor tends to be increased because of a demand to shorten a time required to take an X-ray CT scan of a subject. When a rotor is rotated at a higher rotational speed, the rotor is distorted due to a slight displacement between the rotation center and the gravity center of the rotor, and thus the rotor vibrates in rotation. The vibration of the rotor in rotation puts an X-ray CT scan plane out of position, and thus deteriorates the quality of an image obtained by taking an X-ray CT scan.
Other causes of the vibration of the rotor in rotation include such phenomena that: a base portion of the cantilevered tilt shaft supporting the rotor in a tiltable manner is deformed; the rotor is unevenly supported between its two sides because a drive cylinder configured to tilt the rotor is provided at only one side of the rotor; a base fixed to the floor to support the rotor resonates with the rotation of the rotor.